The present invention relates to an electric brake caliper assembly for a vehicle, and more particularly, to an electric brake caliper with a highly efficient load-producing drive mechanism.
Various types of brake systems are known for use in automotive vehicles. Such brake systems include, for example, hydraulic brakes, anti-lock brakes and electric brakes. Electric brake systems (also referred to as xe2x80x9cbrake by wirexe2x80x9d systems) utilize caliper mechanisms that incorporate an electric motor for driving a gear assembly positioned within the caliper housing, which, in turn, drives an inner brake pad against a brake rotor disc of a vehicle. A second, outer brake pad mounted to the caliper housing is positioned on an opposite side of the rotor disc. During braking, the inner brake pad is forced against the rotor disc and a resulting reactionary force pulls the outer break pad into engagement with the opposite side of the disc. Engagement of the inner and outer brake pads will slow or stop rotation of the rotor disc, and, in turn, slow the vehicle or hold,the vehicle in a fixed position.
A load sensor is typically positioned to detect the amount of force applied by the inner brake pad to the rotor disc. This load sensor is operatively coupled to a mechanism for controlling the position of the caliper housing, and in turn, the force applied by the outer break pad. Accordingly, this mechanism is used to equalize (or xe2x80x9ccenterxe2x80x9d) the force applied by the two brake pads on the rotor disc.
A disadvantage with prior art electric brake calipers is that the design of such electric brake calipers requires that the reduction gears in the drive assembly bear an undesirable amount of the reactionary force from the inner brake pad during braking. If such reactionary force is borne by such reduction gears, it may have a tendency to adversely affect (i.e., xe2x80x9cbog downxe2x80x9d) the operation of such reduction gears. Accordingly, there is a need for an electric brake caliper drive mechanism that minimizes the amount of the reactionary force borne by the reduction gears.
The present invention provides an electric brake caliper with a drive mechanism that minimizes the amount of reactionary force borne by the gear reducers in the drive mechanism. The drive mechanism is also designed to provide high loads with a substantially low pitch.
A first aspect of the present invention provides a brake caliper that includes a caliper housing having a rotor channel adapted to receive a rotor (such as a rotor disc) therein, where the rotor channel has a first axial surface adapted to seat an outer brake pad thereon. The brake caliper also includes a piston assembly mounted to the housing on an axial side of the rotor channel opposite that of the outer brake pad. The piston assembly includes: (a) a piston nut, reciprocatable towards and away from the rotor channel, where the piston nut is adapted to seat an inner brake pad thereon, (b) a cylindrical screw threaded into the piston nut, where the screw includes a coaxial, cylindrical bore extending therein, and (c) a planetary gear train positioned within the cylindrical bore of the screw, where the planetary gear train includes a motor-driven, central sun gear, at least one coaxial tube ring gear and at least one planetary pinion operatively engaged between the sun gear and the tube ring gear and carried on a revolving carrier, where the revolving carrier includes an output shaft extending therefrom, coaxial with, and coupled to the screw. The planetary pinion is axially slidable with respect to the tube ring gear such that any returning force applied by the inner brake pad against the planetary gear train of the piston assembly will be borne primarily by the tube ring gear, and thus, will not substantially adversely affect the operation of the planetary pinion and associated sun gear.
Preferably, the brake caliper also includes a force sensor positioned against a longitudinal end of the tube ring gear opposite that of the inner brake pad. This force sensor is adapted to be coupled to a conventional mechanism for controlling the position of the caliper housing, and in turn, the force applied by the outer brake pad.
The brake caliper also preferably includes a retaining flange extending radially inwardly from a longitudinal end of the piston nut, approximate the inner brake pad. The retaining flange prevents the cylindrical screw from traveling axially beyond a predefined point, thereby protecting the inner brake pad from damage caused by the cylindrical screw contacting the inner brake pad when the piston nut is returning to its home position after the brake caliper has applied a significant load against the rotor. It is also preferred that the inner brake pad includes a plurality of pins extending therefrom and received within the corresponding plurality of pin holes extending into the piston nut. This engagement of pins and pinholes prevents rotation (i.e., xe2x80x9ccockingxe2x80x9d) of the piston nut during actuation of the brake caliper drive mechanism.
In another aspect of the present invention, a brake caliper includes a caliper housing having a rotor channel adapted to receive a rotor therein, where the channel has first axial surface adapted to seat an outer brake pad thereon. The brake caliper also includes a piston assembly mounted to the housing on an axial side of the rotor channel, opposite that of the outer brake pad. The piston assembly includes (a) a piston nut, reciprocatable towards and away from the rotor channel, where the piston nut is adapted to seat an inner brake pad thereon, (b) a cylindrical screw threaded into the piston nut, where the screw includes a coaxial, cylindrical bore extending therein, and (c) a planetary gear train positioned within the cylindrical bore of the screw. The planetary gear train includes: (1) a first motor-driven sun gear, (2) a tube ring gear coaxial with the first sun gear, (3) a first-stage planetary pinion engaged between the first sun gear and the tube ring gear, (4) a revolving stage separator coaxial with the first sun gear and carrying the first planetary pinion for rotation on a radially distal rotational axis, where the stage separator includes a second sun gear extending therefrom, the second sun gear being coaxial with the first sun gear, (4) a second planetary pinion engaged between the second sun gear and the tube ring gear, and (6) a revolving carrier coaxial with the first and second sun gears and carrying the second planetary pinion for rotation on a radially distal rotational axis. The revolving carrier includes a drive shaft extending therefrom, coaxial with the first and second sun gears, and the drive shaft is coaxially coupled to the cylindrical screw; thereby, rotationally driving the cylindrical screw, which, in turn, axially drives the piston nut towards or away from the rotor disc in the rotor channel.
Preferably, the planetary gear train includes three of the first-stage planetary pinions and three of the second-stage planetary pinions, all of which are uniformly distributed about the circumference of their respective sun gears. It is also preferred that the gear train also includes a first trio of washers respectively provided axially between the first-stage planetary pinions and the stage separator, and a second trio of washers respectively provided axially between the second-stage planetary pinions and the revolving carrier. Such washers are provided to reduce wear in the planetary gear train by reducing friction between the planetary pinions and the respective stage separator or carrier. It is also preferred that the planetary gear train also includes an annular washer provided axially between the second-stage planetary pinions and the stage separator, where the annular washer is coaxial with the drive gear. This annular washer is provided to reduce wear between the orbiting second-stage pinions and the revolving stage separator.
Accordingly, it is an object of the present invention to provide a drive mechanism for an electric brake caliper in which the reactionary force applied by the inner brake pad is not borne by the gear reducers therein. It is an object of the present invention to provide a drive mechanism for an electric brake caliper in which wear is reduced in the components of the gear reducer mechanism. It is an object of the present invention to provide an electric brake caliper in which xe2x80x9ccockingxe2x80x9d is reduced between the inner brake pad and the piston of the drive mechanism. It is also an object of the present invention to provide an electric brake caliper in which the drive mechanism includes a ball screw and nut assembly, where the ball screw component of the ball screw and nut assembly is prevented from contacting the inner brake pad when the ball screw and nut assembly is returning to its home position after the brake caliper has applied a significant load against the rotor disc. These and other objects of the present invention will be apparent from the following description, the appended claims and the attached drawings.